Fun with cosmic strings : A CMB Millikan experiment and colliders in the sky

We discuss two unique signatures of cosmic strings.  Photons moving around an axion string undergo an Aharonov-Bohm effect.  As a result, axion strings produce a distinct quantized polarization rotation of CMB photons which can be as large as O(1%).  The quantized polarization rotation angle is topological in nature and its value provides insight into the quantization of electric charge.  On the flip side, axion strings moving through electric and magnetic fields obtain extremely large currents.  When these currents collide, they shine with the brightness of 10^7 suns giving a unique signature that is observable at current and future telescopes.